The present invention relates to a process for preparing an ester, acetal, ketal, ether or alkyl glycoside in the presence of an aluminum catalyst.
To prepare a glycidyl ether, two processes have conventionally been known. The first is one-stage process where an alcohol and an xcex1-epihalohydrin are reacted in the presence of an alkali and a phase transfer catalyst such as a quaternary ammonium salt. The second is a two-stage process where an alcohol is reacted with an xcex1-epihalohydrin in the presence of an acid catalyst and the resulting halohydrin ether is subjected to ring closure with an alkali. In the one-step process, an excess amount of the xcex1-epihalohydrin is required to prevent further addition of the alcohol to the resulting glycidyl ether. In the two-step process, the alcohol must be added in an excess amount relative to the xcex1-epihalohydrin, because the conversion ratio of the alcohol is not high enough in the presence of a bronsted acid catalyst, e.g., sulfuric acid. Furthermore, excessive addition reactions of the xcex1-epihalohydrin to the halohydrin ether occurs when a highly active Lewis acid such as boron trifluoride or tin tetrachloride is used as an acid catalyst. Metal chloride such as aluminum chloride, tin chloride or iron chloride used as a Lewis acid catalyst are problematic because of catalyst deactivation by alcoholysis and the reaction of free chlorine with the xcex1-epihalohydrin. Moreover, in the two-stage process a hydrophilic solvent or phase transfer catalyst must be used in order to efficiently close the halohydrin ether ring with an alkali.
Examples of preparing dialkylglyceryl ether are a process of reacting an alcohol with an xcex1-epihalohydrin in the presence of an alkali and a process of reacting glycerin with an alkyl halide in the presence of an alkali. However, these reactions require alcohol or an alkyl halide to be used in large excess which is problematic because simultaneous introduction of two different alkyl groups is considerably difficult. Although it is possible to obtain a dialkylglyceryl ether containing freely selected alkyl groups if an alcohol and a glycidyl ether are reacted in the presence of an alkali or acid catalyst, using alkali is problematic because an excess alcohol must be used to prevent further reaction of the product whereby the glycidyl ether partially undergoes hydrolysis. Using an acid is also problematic because the glycidyl ether is polymerized during the reaction.
A process for preparing an ester, acetal, ketal, ether or alkyl glycoside by using, as a catalyst, a combination of an aluminum alkoxide and a phenol or sulfonic acid or a compound wherein these two have been bonded is described in WO98/50389. However, the yields obtained by this process were not satisfactory and thus further yield improvements are necessary. Additionally, this process is unsatisfactory because of the significant increase of Chemical Oxygen Demand (COD) in the water layer, thereby burdening waste water disposal.
A process for preparing an alkanol alkoxylate product characterized by a narrow-range alkylene oxide adduct distribution and a low content of a residual alkanol, which comprises reacting an alkylene oxide reactant composed of at least one C2-4 vicinal alkylene oxide with an alkanol reactant composed of at least one C6-36 alkanol in the presence of a catalytically effective amount of a catalyst, where the catalyst was prepared by contacting (i) at least one sulfur-containing acid and (ii) at least one aluminum compound, e.g., aluminum alcoholates or aluminum phenolates (Japanese Patent Application Laid-open No. SHO 62164641). This process aims to prepare a nonionic surfactant by adding a plurality of moles of a C2-4 vicinal alkylene oxide to an alcohol. An ether with only 1 mole of an alkylene oxide is not available by this process.
The present inventors have found that the combination of an aluminum alkoxide and sulfuric acid or phosphoric acid makes it possible to effectively prepare an ester, acetal, ketal, ether or alkyl glycoside and in addition to facilitate waste water disposal without raising the COD in the water layer.
In accordance with this finding, an object of the present invention is a process for preparing an ester, acetal, ketal, ether or alkyl glycoside, which comprises reacting an alcohol with a carbonyl compound, alcohol, olefin, epoxy compound (except C2-4 vicinal alkylene oxide) or saccharide in the presence of (A) an aluminum alkoxide and (B) sulfuric acid or phosphoric acid.
Another object of the present invention is a process for preparing a glyceryl ether, which comprises reacting an alcohol and an xcex1-epihalohydrin in the presence of the above-described catalyst and reacting the ether obtained with an alkali.
Another object of the present invention is a process for preparing a monoalkylglyceryl ether which comprises; hydrolyzing the glycidyl ether thus obtained.
The aluminum alkoxide (A) catalyst can be any aluminum alkoxide in the form of a mono-, di- or tri-alkoxide. Among them, an aluminum trialkoxide is more preferred, with an aluminum tri(C1-4 alkoxide) being particularly preferred. Specific examples of the aluminum alkoxide include aluminum trimethoxide, aluminum triethoxide, aluminum triisopropoxide and aluminum triisobutoxide, with aluminum triisopropoxide being particularly preferred. Commercially available aluminum alkoxides can also be used.
Alternatively, a mixture of mono-, di- and tri-alkoxide forms available by reacting an aluminum trihalide or trialkyl aluminum with an alcohol can be used. In this case, it is preferred to select the conditions permitting the preparation of a mixture having a larger trialkoxide content.
Sulfuric acid or phosphoric acid (B) catalyst efficiently catalyzes the above-described reaction when used in combination with the above-described aluminum alkoxide. The reaction does not proceed in the presence of aluminum sulfate. As the catalyst (B), sulfuric acid is preferred, with concentrated sulfuric acid having a concentration of 90% or greater being more preferred and concentrated sulfuric acid or fuming sulfuric acid having a concentration of 96% or greater being particularly preferred. In the present invention, a combination of aluminum triisopropoxide and sulfuric acid or phosphoric acid is preferred, of which the combination of aluminum triisopropoxide and sulfuric acid is particularly preferred.
Alcohols usable in the present invention include those represented by the following formula (1):
R1xe2x80x94(OA1)mxe2x80x94OHxe2x80x83xe2x80x83(1)
wherein, R1 represents a saturated or unsaturated, linear or branched hydrocarbon group having 1 to 36 carbon atoms in total, A1 represents a C2-4 alkylene group and m is 0 to 100. Specific examples include saturated aliphatic alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, 2-ethylhexanol and 3,5-dimethylhexanol; and unsaturated aliphatic alcohols such as oleyl alcohol and linoleyl alcohol; and alkylene oxide adducts thereof. As such an alkylene oxide adduct, an ethylene oxide adduct (an alcohol of the formula (1) wherein A1 represents ethylene) and the number ((m) in the formula (1)) of moles added is preferably 0 to 20. As alcohols, those free of an alkylene oxide (alcohols of the formula (1) wherein m stands for 0) are preferred.
Examples of the carbonyl compound usable in the present invention include carboxylates, aldehydes and ketones. By the use of, as a raw material, a carboxylate, aldehyde or ketone, the corresponding ester, acetal or ketal can be prepared, respectively. By the reaction of the above-described alcohol with another alcohol, an olefin or an epoxy compound, the corresponding ether can be obtained. Reaction of the above-described alcohol with a saccharide yields the corresponding alkyl glycoside.
Among them, reaction between the alcohol and epoxy compound (except C2-4 vicinal alkylene oxides) is particularly preferred in the present invention. As the epoxy compound, xcex1-epihalohydrins such as xcex1-epichlorohydrin, xcex1-epibromohydrin and xcex1-epiiodohydrin and 1,2-epoxy compounds represented by the following formula (2): 
wherein, R2 represents a hydrogen atom or a saturated or unsaturated, linear or branched C1-24 hydrocarbon group which may have a substituent, A2 represents a C2-4 alkylene group, q stands for 0 to 100, and r is 0 or 1, with the proviso that R2 represents a C1-24 hydrocarbon group when r is 0. Examples of the compound represented by the formula (2) include 1,2-epoxyalkanes such as 1,2,-epoxyhexane, 1,2-epoxyoctane, 1,2-epoxydecane and 1,2-epoxydodecane and alkyl glycidyl ethers such as butyl glycidyl ether, octyl glycidyl ether and dodecyl glycidyl ether and glycidol. Among the epoxy compounds, xcex1-epihalohydrins and glycidol are more preferred.
In the halohydrin-ether forming reaction, the alcohol is preferably added in an amount of 0.5 to 5.0 moles, more preferably 0.5 to 2.0 moles, particularly preferably 0.8 to 1.5 moles per mole of the xcex1-epihalohydrin. The catalyst (A) is preferably added in an amount of 0.001 to 0.1 mole, particularly preferably 0.005 to 0.05 mole per mole of the xcex1-epihalohydrin. When sulfuric acid is employed as the catalyst (B), sulfuric acid is added in an amount of 0.8 to 1.75 moles, more preferably 1.0 to 1.75 moles, particularly preferably 1.25 to 1.5 moles per mole of the catalyst (A). When phosphoric acid is employed as the catalyst (B), phosphoric acid is preferably added in an amount of 0.67 to 1.2 moles, particularly preferably 0.8 to 1.0 time mole per mole of the catalyst (A). The ratio of these catalysts is an important factor in the present reaction. The reaction temperature is 50 to 150xc2x0 C., with 70 to 130xc2x0 C. being particularly preferred. The reaction time is preferably 1 to 5 hours.
The raw material ratio, catalyst ratio and reaction temperature in the reaction of the alcohol with the carbonyl compound, alcohol, olefin or saccharide are similar to those in the reaction of the alcohol with the xcex1-epihalohydrin.
It is preferred to charge the alcohol and the catalysts (A) and (B) and after removal of water, react them with the xcex1-epihalohydrin. The water content in the system is preferably 0.2% or less, with 0.1% or less being more preferred. Removal of water from the system suppresses the polymerization of the xcex1-epihalohydrin, whereby a target halohydrin ether can be obtained in a high yield.
From the halohydrin ether obtained by the above-described reaction, the corresponding glycidyl ether can be prepared by adding, to the halohydrin ether, an alkali without removing the catalysts from the reaction mixture and then effecting ring closure by the hydrogen-halide eliminating reaction.
Examples of alkali include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide and hydroxides of an alkaline earth metal such as calcium hydroxide and barium hydroxide, of which sodium hydroxide and potassium hydroxide are preferred.
In the ring closure reaction of the halohydrin ether, the alkali is preferably added in an amount of 1.0 to 4.0 moles per mole of the amount of the xcex1-eihalohydrin charged, particularly preferred is 1.0 to 2.0 moles per mole of the amount of the xcex1-eihalohydrin charged. For example, it is preferred to add the alkali in the form of a 10 to 50% aqueous solution. The reaction is preferably carried out at 40 to 110xc2x0 C. for 0.5 to 8 hours.
The glycidyl ether thus obtained can he converted into the corresponding monoalkyl glyceryl ether by hydrolysis in a conventional manner. Examples of hydrolysis are disclosed in Japanese patent application laid-open No. 49-86307, wherein hydrolysis of glycidyl ether is carried out in an aqueous solution of aliphatic acid mono or polycarboxylic acid salt, and Japanese patent application laid-open No. 56-133281, wherein a carbonyl compound is added to a glycidyl ether to give a 1,3-dioxolan compound, this compound being subsequently hydrolyzed.
When the compound represented by the formula (2) is employed as the epoxy compound, ethers represented by the following formula (3): 
wherein R2, A2, q and r have the same meanings as described above, and one of R1a and R1b represents a hydrogen atom while the other one represents R1xe2x80x94(OA1)mxe2x80x94 in which R1, A1 and m have the same meanings as described above can be obtained.
The target compounds, for example, glycidyl ethers and alkyl glyceryl ethers, can be isolated and purified by known isolation and purification means, more specifically, distillation, recrystallization or column chromatography.